Sighting devices such as riflescopes have long been used in conjunction with weapons and firearms, such as rifles, handguns, and crossbows, to allow a shooter to accurately aim at a selected target. Because bullet and arrow trajectory, wind conditions, and distance to the target can vary depending upon shooting conditions, quality sighting devices typically provide compensation for variations in these conditions by allowing a shooter to make incremental adjustments to the optical characteristics or the aiming of the sighting device relative to the weapon surface on which it is mounted. These adjustments are known as elevation and windage adjustments, and are typically accomplished by lateral movement of an adjusting member, such as a reticle located within the riflescope, as shown in U.S. Pat. No. 3,058,391 of Leupold, or movement of one or more lenses within a housing of the riflescope, as shown in U.S. Pat. Nos. 3,297,389 and 4,408,842 of Gibson, and U.S. Pat. No. 7,827,723 of Zaderey et al.
The shooter typically makes such adjustments using rotatable adjustment knobs to actuate the adjustable member of the sighting device. In some riflescopes, an index mark on the housing of the riflescope provides a reference by which a shooter may read a scale marked around the circumference of the adjustment knob. These scales typically are finely tuned for specific weapons, weapon types, ammunition characteristics, distances, atmospheric conditions, and a host of other variables. Accordingly, scales tuned for one set of conditions may be inaccurate when used with different ammunition, weapons, geographic elevation, and/or temperature for which the scale was calibrated. Thus, when a shooter faces changes in shooting conditions, the shooter may desire to replace the scale with a suitable scale that is appropriately calibrated to provide the proper reference for the new shooting conditions.
In some systems, such as the assemblies described in U.S. Pat. No. 7,997,163 and U.S. Pat. Pub. No. 2008/0289239, the adjustment knob includes a scale etched, inscribed, or otherwise marked on a portion of the adjustment knob. In such assemblies, the shooter uses a tool to disengage a screw or a pin retaining the knob on the riflescope. The knob is thereafter removed and replaced with a different knob having a properly calibrated scale intended to be used for the new shooting conditions.
Other systems, such as the assembly described in U.S. Pat. No. 8,001,714, use ballistics calculations and other calibration data in conjunction with a label making apparatus to generate a printed label with dial-calibration data customized to different types of projectiles and different shooting conditions. A number of individual labels may be generated with calibration data for different projectiles, shooting conditions, etc. Thereafter, each label may be taped or otherwise affixed around a turret to create a number of customized turrets suitable for different types of projectiles and/or shooting conditions. In a similar system using labels bearing calibration data, such as the system described in U.S. Pat. No. 4,285,137, the labels may simply be removed and replaced on the knob as needed.
The present inventor has recognized a number of disadvantages associated with such riflescope configurations. One disadvantage is that a shooter will have to purchase and carry various knobs for a number of different shooting conditions. In addition, replacing the knob typically requires the shooter to carry and use tools, such as a hex key, to remove and refasten set screws or other fasteners that mount the knob to the riflescope housing, and there is a risk of dropping or losing components during the replacement process.
The present inventor has, thus, recognized a need for an improved knob assembly with an easily exchangeable scale for quickly adjusting to changes in shooting conditions without requiring the use of tools or removing the knob assembly from the riflescope housing to effectuate such exchanges.
Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings.